"Developing a regular sleep routine, consistent wake and bed times that limit screen-time prior to bed, in also an important part of growth, development, and behaviour.

'"In another analysis, we found that children who watched more than 2 hours of screen time per day were almost 65 per cent less likely to sleep 10 hours per day. So more screen time equals less sleep time."

The researchers recommended allowing pre-school kids less than half an hour a day on gadgets - compared to the hour-and-a-half the average three year old spends glued to a screen.